diff mbox series

usb: gadget: pch_udc: Convert to use GPIO descriptors

Message ID 20200627111029.513642-1-linus.walleij@linaro.org
State Superseded
Headers show
Series usb: gadget: pch_udc: Convert to use GPIO descriptors | expand

Commit Message

Linus Walleij June 27, 2020, 11:10 a.m. UTC
This switches the PCH UDC driver to use GPIO descriptors. The way
this is supposed to be used is confusing. The code contains the
following:

    /* GPIO port for VBUS detecting */
    static int vbus_gpio_port = -1; /* GPIO port number (-1:Not used) */

So a hardcoded GPIO number in the code. Further the probe() path
very clearly will exit if the GPIO is not found, so this driver
can only be configured by editing the code, hard-coding a GPIO
number into this variable.

This is simply not how we do things. My guess is that this is
used in products by patching a GPIO number into this variable and
shipping a kernel that is compile-time tailored for the target
system.

I switched this mechanism to using a GPIO descriptor associated
with the parent PCI device. This can be added by using the 16bit
subsystem ID or similar to identify which exact machine we are
running on and what GPIO is present on that machine, and then
add a GPIO descriptor using gpiod_add_lookup_table() from
<linux/gpio/machine.h>. Since I don't have any target systems
I cannot add this but I'm happy to help. I put in a FIXME so
the people actually using this driver knows what to do.

Cc: Felipe Balbi <balbi@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

---
Andy: your input would be appreciated, this kind of code
customizing random embedded Intel systems is deep water for
me, so this is just a rough guess on how it should be done.
---
 drivers/usb/gadget/udc/pch_udc.c | 55 +++++++++++++-------------------
 1 file changed, 22 insertions(+), 33 deletions(-)

-- 
2.25.4

Comments

Andy Shevchenko July 2, 2020, 2:57 p.m. UTC | #1
On Sat, Jun 27, 2020 at 01:10:29PM +0200, Linus Walleij wrote:
> This switches the PCH UDC driver to use GPIO descriptors. The way

> this is supposed to be used is confusing. The code contains the

> following:

> 

>     /* GPIO port for VBUS detecting */

>     static int vbus_gpio_port = -1; /* GPIO port number (-1:Not used) */

> 

> So a hardcoded GPIO number in the code. Further the probe() path

> very clearly will exit if the GPIO is not found, so this driver

> can only be configured by editing the code, hard-coding a GPIO

> number into this variable.

> 

> This is simply not how we do things. My guess is that this is

> used in products by patching a GPIO number into this variable and

> shipping a kernel that is compile-time tailored for the target

> system.

> 

> I switched this mechanism to using a GPIO descriptor associated

> with the parent PCI device. This can be added by using the 16bit

> subsystem ID or similar to identify which exact machine we are

> running on and what GPIO is present on that machine, and then

> add a GPIO descriptor using gpiod_add_lookup_table() from

> <linux/gpio/machine.h>. Since I don't have any target systems

> I cannot add this but I'm happy to help. I put in a FIXME so

> the people actually using this driver knows what to do.

> 

> Cc: Felipe Balbi <balbi@kernel.org>

> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

> ---

> Andy: your input would be appreciated, this kind of code

> customizing random embedded Intel systems is deep water for

> me, so this is just a rough guess on how it should be done.


Linus, I have set up the device (it's actually available as Minnowboard v1) and
will look at this.

For time being there is a patch you need to fold into this (sorry, it's mangled):

(Explanation: GPIO will be locked with request_irq() call)

--- a/drivers/usb/gadget/udc/pch_udc.c
+++ b/drivers/usb/gadget/udc/pch_udc.c
@@ -1367,7 +1367,7 @@ static int pch_vbus_gpio_init(struct pch_udc_dev *dev)
        dev->vbus_gpio.intr = 0;
 
        /* Retrieve the GPIO line from the USB gadget device */
-       gpiod = devm_gpiod_get(dev->gadget.dev.parent, NULL, GPIOD_IN);
+       gpiod = gpiod_get(dev->gadget.dev.parent, NULL, GPIOD_IN);
        if (IS_ERR(gpiod))
                return PTR_ERR(gpiod);
        gpiod_set_consumer_name(gpiod, "pch_vbus");
@@ -1389,6 +1389,7 @@ static int pch_vbus_gpio_init(struct pch_udc_dev *dev)
                                __func__, irq_num, err);
                }
        }
+       gpiod_put(gpiod);
 
        return 0;

> ---

>  drivers/usb/gadget/udc/pch_udc.c | 55 +++++++++++++-------------------

>  1 file changed, 22 insertions(+), 33 deletions(-)

> 

> diff --git a/drivers/usb/gadget/udc/pch_udc.c b/drivers/usb/gadget/udc/pch_udc.c

> index 3344fb8c4181..a9e332130091 100644

> --- a/drivers/usb/gadget/udc/pch_udc.c

> +++ b/drivers/usb/gadget/udc/pch_udc.c

> @@ -12,12 +12,9 @@

>  #include <linux/interrupt.h>

>  #include <linux/usb/ch9.h>

>  #include <linux/usb/gadget.h>

> -#include <linux/gpio.h>

> +#include <linux/gpio/consumer.h>

>  #include <linux/irq.h>

>  

> -/* GPIO port for VBUS detecting */

> -static int vbus_gpio_port = -1;		/* GPIO port number (-1:Not used) */

> -

>  #define PCH_VBUS_PERIOD		3000	/* VBUS polling period (msec) */

>  #define PCH_VBUS_INTERVAL	10	/* VBUS polling interval (msec) */

>  

> @@ -302,13 +299,13 @@ struct pch_udc_ep {

>  /**

>   * struct pch_vbus_gpio_data - Structure holding GPIO informaton

>   *					for detecting VBUS

> - * @port:		gpio port number

> + * @port:		gpio descriptor for the VBUS GPIO

>   * @intr:		gpio interrupt number

>   * @irq_work_fall	Structure for WorkQueue

>   * @irq_work_rise	Structure for WorkQueue

>   */

>  struct pch_vbus_gpio_data {

> -	int			port;

> +	struct gpio_desc	*port;

>  	int			intr;

>  	struct work_struct	irq_work_fall;

>  	struct work_struct	irq_work_rise;

> @@ -1253,7 +1250,7 @@ static int pch_vbus_gpio_get_value(struct pch_udc_dev *dev)

>  	int vbus = 0;

>  

>  	if (dev->vbus_gpio.port)

> -		vbus = gpio_get_value(dev->vbus_gpio.port) ? 1 : 0;

> +		vbus = gpiod_get_value(dev->vbus_gpio.port) ? 1 : 0;

>  	else

>  		vbus = -1;

>  

> @@ -1355,42 +1352,30 @@ static irqreturn_t pch_vbus_gpio_irq(int irq, void *data)

>  /**

>   * pch_vbus_gpio_init() - This API initializes GPIO port detecting VBUS.

>   * @dev:	Reference to the driver structure

> - * @vbus_gpio	Number of GPIO port to detect gpio

>   *

>   * Return codes:

>   *	0: Success

>   *	-EINVAL: GPIO port is invalid or can't be initialized.

>   */

> -static int pch_vbus_gpio_init(struct pch_udc_dev *dev, int vbus_gpio_port)

> +static int pch_vbus_gpio_init(struct pch_udc_dev *dev)

>  {

>  	int err;

>  	int irq_num = 0;

> +	struct gpio_desc *gpiod;

>  

> -	dev->vbus_gpio.port = 0;

> +	dev->vbus_gpio.port = NULL;

>  	dev->vbus_gpio.intr = 0;

>  

> -	if (vbus_gpio_port <= -1)

> -		return -EINVAL;

> -

> -	err = gpio_is_valid(vbus_gpio_port);

> -	if (!err) {

> -		pr_err("%s: gpio port %d is invalid\n",

> -			__func__, vbus_gpio_port);

> -		return -EINVAL;

> -	}

> -

> -	err = gpio_request(vbus_gpio_port, "pch_vbus");

> -	if (err) {

> -		pr_err("%s: can't request gpio port %d, err: %d\n",

> -			__func__, vbus_gpio_port, err);

> -		return -EINVAL;

> -	}

> +	/* Retrieve the GPIO line from the USB gadget device */

> +	gpiod = devm_gpiod_get(dev->gadget.dev.parent, NULL, GPIOD_IN);

> +	if (IS_ERR(gpiod))

> +		return PTR_ERR(gpiod);

> +	gpiod_set_consumer_name(gpiod, "pch_vbus");

>  

> -	dev->vbus_gpio.port = vbus_gpio_port;

> -	gpio_direction_input(vbus_gpio_port);

> +	dev->vbus_gpio.port = gpiod;

>  	INIT_WORK(&dev->vbus_gpio.irq_work_fall, pch_vbus_gpio_work_fall);

>  

> -	irq_num = gpio_to_irq(vbus_gpio_port);

> +	irq_num = gpiod_to_irq(gpiod);

>  	if (irq_num > 0) {

>  		irq_set_irq_type(irq_num, IRQ_TYPE_EDGE_BOTH);

>  		err = request_irq(irq_num, pch_vbus_gpio_irq, 0,

> @@ -1416,9 +1401,6 @@ static void pch_vbus_gpio_free(struct pch_udc_dev *dev)

>  {

>  	if (dev->vbus_gpio.intr)

>  		free_irq(dev->vbus_gpio.intr, dev);

> -

> -	if (dev->vbus_gpio.port)

> -		gpio_free(dev->vbus_gpio.port);

>  }

>  

>  /**

> @@ -2894,7 +2876,7 @@ static int pch_udc_pcd_init(struct pch_udc_dev *dev)

>  {

>  	pch_udc_init(dev);

>  	pch_udc_pcd_reinit(dev);

> -	pch_vbus_gpio_init(dev, vbus_gpio_port);

> +	pch_vbus_gpio_init(dev);

>  	return 0;

>  }

>  

> @@ -3096,6 +3078,13 @@ static int pch_udc_probe(struct pci_dev *pdev,

>  

>  	dev->base_addr = pcim_iomap_table(pdev)[bar];

>  

> +	/*

> +	 * FIXME: add a GPIO descriptor table to pdev.dev using

> +	 * gpiod_add_descriptor_table() from <linux/gpio/machine.h> based on

> +	 * the PCI subsystem ID. The system-dependent GPIO is necessary for

> +	 * VBUS operation.

> +	 */

> +

>  	/* initialize the hardware */

>  	if (pch_udc_pcd_init(dev))

>  		return -ENODEV;

> -- 

> 2.25.4

> 


-- 
With Best Regards,
Andy Shevchenko
Linus Walleij July 16, 2020, 8:44 a.m. UTC | #2
On Thu, Jul 2, 2020 at 4:57 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:

> > Andy: your input would be appreciated, this kind of code

> > customizing random embedded Intel systems is deep water for

> > me, so this is just a rough guess on how it should be done.

>

> Linus, I have set up the device (it's actually available as Minnowboard v1) and

> will look at this.


OK whenever you have time, there is no hurry.

> For time being there is a patch you need to fold into this (sorry, it's mangled):

>

> (Explanation: GPIO will be locked with request_irq() call)


I do not understand this, sadly. gpiod_lock_as_irq() will be called
indeed, but we are requesting it as input and keeping it as such
so this should be fine?

Yours,
Linus Walleij
Andy Shevchenko July 16, 2020, 10:19 a.m. UTC | #3
On Thu, Jul 16, 2020 at 11:49 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>

> On Thu, Jul 2, 2020 at 4:57 PM Andy Shevchenko

> <andriy.shevchenko@linux.intel.com> wrote:

>

> > > Andy: your input would be appreciated, this kind of code

> > > customizing random embedded Intel systems is deep water for

> > > me, so this is just a rough guess on how it should be done.

> >

> > Linus, I have set up the device (it's actually available as Minnowboard v1) and

> > will look at this.

>

> OK whenever you have time, there is no hurry.

>

> > For time being there is a patch you need to fold into this (sorry, it's mangled):

> >

> > (Explanation: GPIO will be locked with request_irq() call)

>

> I do not understand this, sadly. gpiod_lock_as_irq() will be called

> indeed, but we are requesting it as input and keeping it as such

> so this should be fine?


When you clean up GPIO at the same time you don't need to carry this
memory and resource for the entire lifetime of the driver. When you
lock it as IRQ the resource is not available to use by others anyway
and will be requested whenever IRQ is requested. That's how I
understand it. And to me it makes sense from a flexibility point of
view and debugging perspective.


-- 
With Best Regards,
Andy Shevchenko
Andy Shevchenko July 19, 2020, 11:29 a.m. UTC | #4
On Thu, Jul 16, 2020 at 01:19:32PM +0300, Andy Shevchenko wrote:
> On Thu, Jul 16, 2020 at 11:49 AM Linus Walleij <linus.walleij@linaro.org> wrote:

> > On Thu, Jul 2, 2020 at 4:57 PM Andy Shevchenko

> > <andriy.shevchenko@linux.intel.com> wrote:

> >

> > > > Andy: your input would be appreciated, this kind of code

> > > > customizing random embedded Intel systems is deep water for

> > > > me, so this is just a rough guess on how it should be done.

> > >

> > > Linus, I have set up the device (it's actually available as Minnowboard v1) and

> > > will look at this.

> >

> > OK whenever you have time, there is no hurry.

> >

> > > For time being there is a patch you need to fold into this (sorry, it's mangled):

> > >

> > > (Explanation: GPIO will be locked with request_irq() call)

> >

> > I do not understand this, sadly. gpiod_lock_as_irq() will be called

> > indeed, but we are requesting it as input and keeping it as such

> > so this should be fine?

> 

> When you clean up GPIO at the same time you don't need to carry this

> memory and resource for the entire lifetime of the driver. When you

> lock it as IRQ the resource is not available to use by others anyway

> and will be requested whenever IRQ is requested. That's how I

> understand it. And to me it makes sense from a flexibility point of

> view and debugging perspective.


I looked closer to the code, it's using it as IRQ and as a GPIO (to know was it
rising or falling). Easier to leave as in your patch. Meanwhile I'm trying to
find some information about actual presence / use of VBUS on Intel Galileo Gen
2 and / or Minnowboard v1.0.

-- 
With Best Regards,
Andy Shevchenko
Andy Shevchenko July 20, 2020, 10:46 a.m. UTC | #5
On Sat, Jun 27, 2020 at 01:10:29PM +0200, Linus Walleij wrote:
> This switches the PCH UDC driver to use GPIO descriptors. The way

> this is supposed to be used is confusing. The code contains the

> following:

> 

>     /* GPIO port for VBUS detecting */

>     static int vbus_gpio_port = -1; /* GPIO port number (-1:Not used) */

> 

> So a hardcoded GPIO number in the code. Further the probe() path

> very clearly will exit if the GPIO is not found, so this driver

> can only be configured by editing the code, hard-coding a GPIO

> number into this variable.

> 

> This is simply not how we do things. My guess is that this is

> used in products by patching a GPIO number into this variable and

> shipping a kernel that is compile-time tailored for the target

> system.

> 

> I switched this mechanism to using a GPIO descriptor associated

> with the parent PCI device. This can be added by using the 16bit

> subsystem ID or similar to identify which exact machine we are

> running on and what GPIO is present on that machine, and then

> add a GPIO descriptor using gpiod_add_lookup_table() from

> <linux/gpio/machine.h>. Since I don't have any target systems

> I cannot add this but I'm happy to help. I put in a FIXME so

> the people actually using this driver knows what to do.


In the future I will submit a patch to fix below FIXME since I found the means
of testing, but it requires some time. Meanwhile I have tested on two Intel
platforms with such UDC and found no regressions

Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>


Felipe, I'm fine with this patch, please proceed if it's okay.

> Cc: Felipe Balbi <balbi@kernel.org>

> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

> ---

> Andy: your input would be appreciated, this kind of code

> customizing random embedded Intel systems is deep water for

> me, so this is just a rough guess on how it should be done.

> ---

>  drivers/usb/gadget/udc/pch_udc.c | 55 +++++++++++++-------------------

>  1 file changed, 22 insertions(+), 33 deletions(-)

> 

> diff --git a/drivers/usb/gadget/udc/pch_udc.c b/drivers/usb/gadget/udc/pch_udc.c

> index 3344fb8c4181..a9e332130091 100644

> --- a/drivers/usb/gadget/udc/pch_udc.c

> +++ b/drivers/usb/gadget/udc/pch_udc.c

> @@ -12,12 +12,9 @@

>  #include <linux/interrupt.h>

>  #include <linux/usb/ch9.h>

>  #include <linux/usb/gadget.h>

> -#include <linux/gpio.h>

> +#include <linux/gpio/consumer.h>

>  #include <linux/irq.h>

>  

> -/* GPIO port for VBUS detecting */

> -static int vbus_gpio_port = -1;		/* GPIO port number (-1:Not used) */

> -

>  #define PCH_VBUS_PERIOD		3000	/* VBUS polling period (msec) */

>  #define PCH_VBUS_INTERVAL	10	/* VBUS polling interval (msec) */

>  

> @@ -302,13 +299,13 @@ struct pch_udc_ep {

>  /**

>   * struct pch_vbus_gpio_data - Structure holding GPIO informaton

>   *					for detecting VBUS

> - * @port:		gpio port number

> + * @port:		gpio descriptor for the VBUS GPIO

>   * @intr:		gpio interrupt number

>   * @irq_work_fall	Structure for WorkQueue

>   * @irq_work_rise	Structure for WorkQueue

>   */

>  struct pch_vbus_gpio_data {

> -	int			port;

> +	struct gpio_desc	*port;

>  	int			intr;

>  	struct work_struct	irq_work_fall;

>  	struct work_struct	irq_work_rise;

> @@ -1253,7 +1250,7 @@ static int pch_vbus_gpio_get_value(struct pch_udc_dev *dev)

>  	int vbus = 0;

>  

>  	if (dev->vbus_gpio.port)

> -		vbus = gpio_get_value(dev->vbus_gpio.port) ? 1 : 0;

> +		vbus = gpiod_get_value(dev->vbus_gpio.port) ? 1 : 0;

>  	else

>  		vbus = -1;

>  

> @@ -1355,42 +1352,30 @@ static irqreturn_t pch_vbus_gpio_irq(int irq, void *data)

>  /**

>   * pch_vbus_gpio_init() - This API initializes GPIO port detecting VBUS.

>   * @dev:	Reference to the driver structure

> - * @vbus_gpio	Number of GPIO port to detect gpio

>   *

>   * Return codes:

>   *	0: Success

>   *	-EINVAL: GPIO port is invalid or can't be initialized.

>   */

> -static int pch_vbus_gpio_init(struct pch_udc_dev *dev, int vbus_gpio_port)

> +static int pch_vbus_gpio_init(struct pch_udc_dev *dev)

>  {

>  	int err;

>  	int irq_num = 0;

> +	struct gpio_desc *gpiod;

>  

> -	dev->vbus_gpio.port = 0;

> +	dev->vbus_gpio.port = NULL;

>  	dev->vbus_gpio.intr = 0;

>  

> -	if (vbus_gpio_port <= -1)

> -		return -EINVAL;

> -

> -	err = gpio_is_valid(vbus_gpio_port);

> -	if (!err) {

> -		pr_err("%s: gpio port %d is invalid\n",

> -			__func__, vbus_gpio_port);

> -		return -EINVAL;

> -	}

> -

> -	err = gpio_request(vbus_gpio_port, "pch_vbus");

> -	if (err) {

> -		pr_err("%s: can't request gpio port %d, err: %d\n",

> -			__func__, vbus_gpio_port, err);

> -		return -EINVAL;

> -	}

> +	/* Retrieve the GPIO line from the USB gadget device */

> +	gpiod = devm_gpiod_get(dev->gadget.dev.parent, NULL, GPIOD_IN);

> +	if (IS_ERR(gpiod))

> +		return PTR_ERR(gpiod);

> +	gpiod_set_consumer_name(gpiod, "pch_vbus");

>  

> -	dev->vbus_gpio.port = vbus_gpio_port;

> -	gpio_direction_input(vbus_gpio_port);

> +	dev->vbus_gpio.port = gpiod;

>  	INIT_WORK(&dev->vbus_gpio.irq_work_fall, pch_vbus_gpio_work_fall);

>  

> -	irq_num = gpio_to_irq(vbus_gpio_port);

> +	irq_num = gpiod_to_irq(gpiod);

>  	if (irq_num > 0) {

>  		irq_set_irq_type(irq_num, IRQ_TYPE_EDGE_BOTH);

>  		err = request_irq(irq_num, pch_vbus_gpio_irq, 0,

> @@ -1416,9 +1401,6 @@ static void pch_vbus_gpio_free(struct pch_udc_dev *dev)

>  {

>  	if (dev->vbus_gpio.intr)

>  		free_irq(dev->vbus_gpio.intr, dev);

> -

> -	if (dev->vbus_gpio.port)

> -		gpio_free(dev->vbus_gpio.port);

>  }

>  

>  /**

> @@ -2894,7 +2876,7 @@ static int pch_udc_pcd_init(struct pch_udc_dev *dev)

>  {

>  	pch_udc_init(dev);

>  	pch_udc_pcd_reinit(dev);

> -	pch_vbus_gpio_init(dev, vbus_gpio_port);

> +	pch_vbus_gpio_init(dev);

>  	return 0;

>  }

>  

> @@ -3096,6 +3078,13 @@ static int pch_udc_probe(struct pci_dev *pdev,

>  

>  	dev->base_addr = pcim_iomap_table(pdev)[bar];

>  

> +	/*

> +	 * FIXME: add a GPIO descriptor table to pdev.dev using

> +	 * gpiod_add_descriptor_table() from <linux/gpio/machine.h> based on

> +	 * the PCI subsystem ID. The system-dependent GPIO is necessary for

> +	 * VBUS operation.

> +	 */

> +

>  	/* initialize the hardware */

>  	if (pch_udc_pcd_init(dev))

>  		return -ENODEV;

> -- 

> 2.25.4

> 


-- 
With Best Regards,
Andy Shevchenko
diff mbox series

Patch

diff --git a/drivers/usb/gadget/udc/pch_udc.c b/drivers/usb/gadget/udc/pch_udc.c
index 3344fb8c4181..a9e332130091 100644
--- a/drivers/usb/gadget/udc/pch_udc.c
+++ b/drivers/usb/gadget/udc/pch_udc.c
@@ -12,12 +12,9 @@ 
 #include <linux/interrupt.h>
 #include <linux/usb/ch9.h>
 #include <linux/usb/gadget.h>
-#include <linux/gpio.h>
+#include <linux/gpio/consumer.h>
 #include <linux/irq.h>
 
-/* GPIO port for VBUS detecting */
-static int vbus_gpio_port = -1;		/* GPIO port number (-1:Not used) */
-
 #define PCH_VBUS_PERIOD		3000	/* VBUS polling period (msec) */
 #define PCH_VBUS_INTERVAL	10	/* VBUS polling interval (msec) */
 
@@ -302,13 +299,13 @@  struct pch_udc_ep {
 /**
  * struct pch_vbus_gpio_data - Structure holding GPIO informaton
  *					for detecting VBUS
- * @port:		gpio port number
+ * @port:		gpio descriptor for the VBUS GPIO
  * @intr:		gpio interrupt number
  * @irq_work_fall	Structure for WorkQueue
  * @irq_work_rise	Structure for WorkQueue
  */
 struct pch_vbus_gpio_data {
-	int			port;
+	struct gpio_desc	*port;
 	int			intr;
 	struct work_struct	irq_work_fall;
 	struct work_struct	irq_work_rise;
@@ -1253,7 +1250,7 @@  static int pch_vbus_gpio_get_value(struct pch_udc_dev *dev)
 	int vbus = 0;
 
 	if (dev->vbus_gpio.port)
-		vbus = gpio_get_value(dev->vbus_gpio.port) ? 1 : 0;
+		vbus = gpiod_get_value(dev->vbus_gpio.port) ? 1 : 0;
 	else
 		vbus = -1;
 
@@ -1355,42 +1352,30 @@  static irqreturn_t pch_vbus_gpio_irq(int irq, void *data)
 /**
  * pch_vbus_gpio_init() - This API initializes GPIO port detecting VBUS.
  * @dev:	Reference to the driver structure
- * @vbus_gpio	Number of GPIO port to detect gpio
  *
  * Return codes:
  *	0: Success
  *	-EINVAL: GPIO port is invalid or can't be initialized.
  */
-static int pch_vbus_gpio_init(struct pch_udc_dev *dev, int vbus_gpio_port)
+static int pch_vbus_gpio_init(struct pch_udc_dev *dev)
 {
 	int err;
 	int irq_num = 0;
+	struct gpio_desc *gpiod;
 
-	dev->vbus_gpio.port = 0;
+	dev->vbus_gpio.port = NULL;
 	dev->vbus_gpio.intr = 0;
 
-	if (vbus_gpio_port <= -1)
-		return -EINVAL;
-
-	err = gpio_is_valid(vbus_gpio_port);
-	if (!err) {
-		pr_err("%s: gpio port %d is invalid\n",
-			__func__, vbus_gpio_port);
-		return -EINVAL;
-	}
-
-	err = gpio_request(vbus_gpio_port, "pch_vbus");
-	if (err) {
-		pr_err("%s: can't request gpio port %d, err: %d\n",
-			__func__, vbus_gpio_port, err);
-		return -EINVAL;
-	}
+	/* Retrieve the GPIO line from the USB gadget device */
+	gpiod = devm_gpiod_get(dev->gadget.dev.parent, NULL, GPIOD_IN);
+	if (IS_ERR(gpiod))
+		return PTR_ERR(gpiod);
+	gpiod_set_consumer_name(gpiod, "pch_vbus");
 
-	dev->vbus_gpio.port = vbus_gpio_port;
-	gpio_direction_input(vbus_gpio_port);
+	dev->vbus_gpio.port = gpiod;
 	INIT_WORK(&dev->vbus_gpio.irq_work_fall, pch_vbus_gpio_work_fall);
 
-	irq_num = gpio_to_irq(vbus_gpio_port);
+	irq_num = gpiod_to_irq(gpiod);
 	if (irq_num > 0) {
 		irq_set_irq_type(irq_num, IRQ_TYPE_EDGE_BOTH);
 		err = request_irq(irq_num, pch_vbus_gpio_irq, 0,
@@ -1416,9 +1401,6 @@  static void pch_vbus_gpio_free(struct pch_udc_dev *dev)
 {
 	if (dev->vbus_gpio.intr)
 		free_irq(dev->vbus_gpio.intr, dev);
-
-	if (dev->vbus_gpio.port)
-		gpio_free(dev->vbus_gpio.port);
 }
 
 /**
@@ -2894,7 +2876,7 @@  static int pch_udc_pcd_init(struct pch_udc_dev *dev)
 {
 	pch_udc_init(dev);
 	pch_udc_pcd_reinit(dev);
-	pch_vbus_gpio_init(dev, vbus_gpio_port);
+	pch_vbus_gpio_init(dev);
 	return 0;
 }
 
@@ -3096,6 +3078,13 @@  static int pch_udc_probe(struct pci_dev *pdev,
 
 	dev->base_addr = pcim_iomap_table(pdev)[bar];
 
+	/*
+	 * FIXME: add a GPIO descriptor table to pdev.dev using
+	 * gpiod_add_descriptor_table() from <linux/gpio/machine.h> based on
+	 * the PCI subsystem ID. The system-dependent GPIO is necessary for
+	 * VBUS operation.
+	 */
+
 	/* initialize the hardware */
 	if (pch_udc_pcd_init(dev))
 		return -ENODEV;